PB1715 EXTRAMEDULLARY LOCALIZATIONS IN ACUTE MYELOID LEUKEMIA. AN EIGHT‐YEARS MONOCENTRIC EXPERIENCE

Background: The incidence, risk factors and prognostic significance of extramedullary involvement (EMI) in adult patients (pts) with acute myeloid leukemia (AML) have not been established yet. Aims: This study analyzes the clinical and biological characteristics, the impact on prognosis and the cumulative incidence of EMI in a monocentric retrospective study. Methods: All consecutive adult pts (aged over 18y.o.) with a diagnosis of AML observed in our institution between January 2010 and December 2017 were included into the analysis. All cases of EMI were registered; only pts who experienced EMI at the onset of AML and receiving induction treatment were evaluated for disease free survival (DFS) and overall survival (OS) Results: Overall 346 AMLs were analyzed. The incidence of EMI was 11% (38 pts). The involved sites were: skin (66%), CNS (23%), pleura (7%), lymph nodes (5%), peritoneum (2%), spleen (2%), pancreas (2%), breasts (2%) and bones (2%). Most pts (91%) had only one site of EMI, while 9% had multiple sites affected at the same time. Twenty‐eight (74%) pts showed signs of EMI at presentation of AML, while in the remaining 10 cases extramedullary involvement occurred at relapse (26%). Cytogenetic, molecular, clinical and laboratory parameters were analyzed in order to identify risk factors. EMI had a significantly higher frequency in pts with monocytic and myelo‐monocytic leukemia subtypes (p < 0,0001), MLL rearrangements (p = 0.001), trisomy 8 (p = 0,02) and a specific cytofluorimetry pattern (CD117‐, p = 0,03; CD56‐/CD117‐, p = 0,04; CD56 + /CD117‐, p = 0,04). In the present study we analyzed only the 28 EMI pts who experienced EMI at the onset of AML; for these pts type of induction treatment, DFS and OS were evaluated. All 28 EMI pts but one were treated with conventional chemotherapy (21 pts), hypomethylating agent (5 pts) or low dose citarabine (1 pts). Eight pts (28.5%) received a consolidation therapy with allogeneic stem cell transplantation (allo‐HSCT). One elderly patient receiving best supportive care, due to poor performance status, was excluded from the analysis. Complete remission (CR) rate after induction therapy of these 27 EMI pts was 22% with a median DFS of 7.4 months (range 2‐79). The median OS of all 27 EMI pts was 11.6 months (range 2‐79); median OS of 8 EMI pts who undergone allo‐HSCT resulted of 16.7 months which was significantly longer than OS of the remaining 19 EMI pts who did not receive transplant (8.2 months) (p = 0.02). No differences emerged in OS according to site of EMI (CNS vs other sites, p 0.43) Univariate and multivariate analyses showed that undergoing allo‐HSCT was the main positive prognostic factors for survivor in our population (p < 0,0001, IC 0,25‐0,48). Summary/Conclusion: These data show a higher incidence of EMI than previously reported in other studies and describe several molecular, morphological, cytogenetic, and cytofluorimetric risk factors associated with EMI. Poor prognosis is confirmed for EMI pts with a median OS lower than 1 years. The allo‐HSCT, applicable however only in some cases, seems to have a crucial role in the therapeutic approach of these pts, being associated with a better prognosis.